The present invention relates to data processing systems. More particularly, it relates to such systems which reserve resources for multimedia connections or sessions.
It has long been known to provide computer systems coupled together by means of digital communication networks so that users of the individual workstations may communicate with one another over the network. More recently, desktop conferencing, remote presentations, and other multimedia applications have been proposed between network users. However, such multimedia applications, as they are associated with data-intensive sound, voice, and video flows, require concomminant high bandwidth communication links between distributed computing systems with minimal communication delay, maximum throughput, and instantaneous burst communication capability. The requirements of such multimedia applications make scheduling appropriate resources to provide for necessary quality of service for multimedia traffic while maintaining network availability for normal bandwidth traffic very difficult.
It is recognized that certain data in a network, such as that associated with multimedia, may require priority handling. A "quality of service" has been defined in the literature, which seeks to describe various parameters which may be specified to define certain minimum requirements which must be met for transmission of given data types over the network. See, for example, quality of service standards set forth in the OSI TP4 interface (publication reference:) and the quality of service standards defined in CCITTQ.931 (ISDN), Q.933 (frame relay), and Q.93B (B-ISDN ATM) drafts. As yet another example, there is a priority mechanism in the IEEE 802.5 specification for the Token Ring network. A station on the ring with a high priority frame to send may indicate this in an access control field of a passing frame. When a station sending the frame releases the token, it releases the token at the priority of the AC field, and eventually sets it back to its original priority as specified in an IEEE 802.5 medium access control protocol. The IEEE standard and implementations thereof merely specify a protocol for increasing and decreasing priority, but each station is unconstrained in its use of priority beyond this protocol.
This in turn gives rise to a serious problem associated with the prior art. In seeking to accommodate situations in which a high priority channel is required to guarantee real time service for multimedia traffic, one approach, since each station is unconstrained, has been for users to indiscriminately increase the priority of their flows to the point where no guarantees for multimedia quality of service were possible in that no discrimination was being provided, e.g., all the users were simply increasing their priorities. This also has the effect of choking off normal nonpriority traffic entirely.
As yet another example of this, unconstrained use of priorities has resulted in bridges and routers loading so much high priority data on them as to flood the token ring with this priority traffic such that multimedia traffic obtains no guaranteed priority. Again, this results from no discrimination between differing connections, sessions, and transmit operations.
Clearly other instances in the communication art have recognized the notion of need for differing priority of data types, whether in the form of multiple channels with different priorities (such as the IBM LAN Streamer Token Ring Adapter Card with two transmit channels, and the 100M BPS Ethernet System with priority channels) and the synchronous/synchronous approach of, for example, the FDDI standards, a representative example of which is the FDDI SMT 7.X.
Moreover, it is clear in the literature that the notion of scheduling data in differing priorities is well known. See for example Liu and Layland, Scheduling Algorithms For Multiprogramming in a Hard-Real-Time Environment, Journal of the Association for Computing Machinery, Vol. 20, #1, January, 1973, where "ratemonotonic priority assignment" is discussed, page 50. Also see, for example, Dominico Ferrari, A Scheme for Real Time Channel Establishment in Wide Area Networks, IEEE Journal of Selected Areas in Communications, Vol. 8, #3, April, 1990, page 368. In this reference modification of an earliest due date (EDD) policy is presented which governs differing levels of priority assigned to tasks.
Similarly, the notion of specifying performance requirements in real time communication services is further addressed in another reference to Dominico Ferrari, Client Requirements for Real-Time Communication Services, IEEE Communications Magazine, November 1990, page 65, wherein it is noted that a client and server will negotiate a specification for their respective requirements for services including delay bounds, throughput bounds, and the like.
The situation is complex. Computer system devices such as network adapters, buses, disks and host processors are diverse in their capabilities in ways that are not easily captured by device specifications. A Priority Token Ring adapter, for example, will be able to reserve more bandwidth for multimedia applications if it can capture a token immediately after releasing it. A Token Ring adapter which cannot capture its token immediately upon releasing it will give other stations on the ring more opportunities to capture the token and thereby reduce the amount of ring bandwidth which a computer serviced by the slow adapter can reserve. This capability is influenced by the speed of the processor, the number of pad symbols introduced onto the ring following a transmission, and other factors which make it difficult predict what guarantees can be provided to multimedia streams.
Just as devices have a wide variety of capabilities, multimedia steams have a great variety of rates: CD-ROM audio may stream data at 175 kilobytes per seconds (KBps), compressed, digital video may run at 150 KBps or greater while still frame audio rates are about 35 kilobytes per second or less. Multimedia computers may also have a variety of delay and burst requirements depending upon configuration.
Thus, whatever means is devised to automatically reserve system or network resources to high bandwidth traffic is likely to be nonoptimal, particularly as new technologies and multimedia file types evolve. Too much multimedia traffic for the reserved resources will result in overutilization causing glitches or jitter in the multimedia sessions. If too much resource is reserved for multimedia traffic to solve the problem above, normal data traffic will be prevented from transmission. The applicants have recognized a need to adjust the allocation of resources devoted to a multimedia session. Further, because a human being is the most adaptable control means yet devised, the applicants propose a user interface operable by the network administrator or other system user. The interface allows one to adjust a default or calculated maximum resource reservation value to a new value to better optimize performance.